Power cycling upstream cable modem when the internet goes down

[johnpoz]

If you were using unifi controller, ie you had some unifi AP for example - then this would do exactly what your asking for

https://store.ui.com/collections/unifi-accessories/products/unifi-smart-power
The UniFi SmartPower Plug is a device installed between the AC outlet and the power plug of an internet modem or router. The UniFi Network Controller continuously monitors availability of an internet connection. If the connection drops, the UniFi SmartPower Plug automatically restarts the modem or router by disconnecting power for a short period of time.

But yeah with all the smart plugs these days, I would think it would be pretty easy to rig something like this up..